Beyond 2,5-furandicarboxylic acid: status quo, environmental assessment, and blind spots of furanic monomers for bio-based polymers†

Since 5-(hydroxymethyl)furfural (HMF) has been labelled as the “sleeping giant” of the bio-based platform-chemical realm, numerous investigations have been devoted to the exploitation of this versatile molecule and its endless chemical transformations into novel monomers for producing bio-based polymers. However, beyond 2,5-furandicarboxylic acid (2,5-FDCA), little attention has been devoted to key aspects that deserve being addressed before bringing forward other HMF-derivatives into the bio-based plastic market, i.e., procedures, scaling-up of the syntheses, products’ purification, physical–thermal properties, and above all green metrics (sustainability/greenness of procedures). This critical review focuses on the most investigated derivatives of HMF beyond 2,5-FDCA, assessing their exploitation as monomers for bio-based polymers. HMF-derived compounds have been classified according to their functionalities, i.e., aldehyde-, diol-, polyol-, amine-, acid-, ester-, carbonate-, acrylate-, and epoxy-based monomers. The related synthetic approaches are discussed, evaluating the sustainability of the procedures reported so far, based on green metrics such as the environmental factor (E-factor) and the process mass intensity (PMI). For each family of HMF derivatives, their use as monomers for the synthesis of bio-based polymers has been addressed, taking into consideration the efficiency of the polymerisation reactions, the physical–chemical and thermal properties of the resulting bio-based polymers, as well as their biodegradability if applicable. The overall picture that emerges is that much has been achieved for the synthesis of furan monomers; however, many obstacles still need to be overcome prior to massively introducing these compounds into the bio-based plastic market. Hopefully, the data reported in this review will shed light on the goals achieved so far, and on some critical issues that must still be tackled in the short- or medium-term for a more sustainable and however efficient industrial process.